There are different types of wireless communication systems. For example, some wireless communication systems include general packet radio service (GPRS), global system for mobile (GSM)/enhanced data rates for GSM evolution (EDGE) radio access network (GERAN), and the newly introduced long term evolution (LTE) evolved universal terrestrial radio access network (EUTRAN). LTE/EUTRAN system has a different physical layer and a different architecture from those systems preceding it, i.e., GPRS, GERAN, or UTRAN.
When a Multi-mode mobile unit is traveling across the geographic coverage of these different systems, it may need to be handed off from one network to another. Since not all networks are identical, a method for supporting the handover between systems would be beneficial.
FIG. 1 shows an exemplary diagram of a system 100 including an LTE system architecture. The system 100 shows an LTE/EUTRAN 101 and its evolved packet core 105 interworking with an existing GERAN 102, UTRAN 103, and their GPRS Core 104. The LTE/EUTRAN 101 comprises an E-Node B (not shown) that is connected (S1) to an evolved packet core 105 containing a mobility management entity/user plane entity (MME/UPE) 106 and an inter AS anchor Gateway 107. The Evolved Packet Core 105 connects (S6) to a home subscriber service (HSS) 111, and connects (S7) to a Policy and Charging Rules (PCRF) 112. The inter AS Anchor gateway 107 connects (Gi) to Operator IP Servers (such as IMS, PSS) 110, connects (S2) to a Non-3GPP IP Access network 108, and connects (S2) to a WLAN 3GPP IP Access network 109. The GPRS Core 104 comprises a Serving GPRS Support Node (SGSN) (not shown) which is responsible for Mobility Management, Access Procedures, and User Plane Control. The GPRS Core 104 also comprises a Gateway GPRS Support Node (GGSN), where the network is connected to external networks and other operator servers. The Operator IP Servers 110 may include an IP Multimedia Service Subsystem (IMS) where VoIP and other multimedia services are controlled. The Non-3GPP IP access network 108 includes connections to other technologies that are developed in other standard Forums such as 3GPP2 (CDMA2000) and WiMAX (IEEE 802.16 system). The WLAN 3GPP IP access network 109 has WLANs incorporated into 3GPP systems via interworking architecture defined in 3GPP.